In automotive vehicles, sliding materials play a role in imparting high wear resistance and low friction coefficients to engine sliding parts under extreme friction/wear conditions. It has recently been attempted to apply various hard thin film materials and roller rocker arms with roller needle bearings to follower parts such as valve lifters and lifter shims.
Hard carbon materials, in particular diamond-like carbon (DLC) materials, are expected as low-friction sliding materials due to the fact that the hard carbon materials generally show low friction coefficients in the air in the absence of lubricating oils than those of wear-resistant hard coating materials such as titanium nitride (TiN) and chromium nitride (CrN).
Further, Patent Document 1 discloses a sliding mechanism that attains low-friction characteristics by the use of sliding members, at least one of which has a hard carbon coating formed of DLC with a hydrogen content of 20 atomic % or less, in combination with a grease containing an ester oil, an ether oil or a mixture thereof as a base oil.
There has however been a demand to achieve further friction reduction in terms of resource conservation and energy conservation. It is accordingly an object of the present invention to provide a sliding mechanism capable of showing a lower friction coefficient for friction reduction and, at the same time, improving in wear resistance and a grease composition for use in such a sliding mechanism.